My usual rules of thumb for CAPTCHA which work at Internet scale are:
1. Algorithmically generated puzzles which are hard for algorithms to
solve (one-way transforms)
Likewise, puzzles which are reasonably possible for real people to
solve
2. Puzzles which do not require localization
3. Puzzles which are not susceptible to brute force attacks (high random
success rates)
That said, it should be obvious that swirled character image captchas
will not work for those with vision impairments but this is easily
remedied with an audio version. Audio and image recognition are pretty
much the two areas that algorithms have trouble with. Common solution is
multiple people speaking on top of each other. Hard for algorithms to
crack but not impossible for real people. Playback using Sound Manager 2
http://www.schillmania.com/projects/soundmanager2/
does the heavy lifting to select native html5 or flash for the audio and
do it in a way that works for all browsers. Other than that they just
have to make sure that the audio play button is easily found in the tab
order and, once pressed, moves focus to the text input. Not much else
needed beyond that.
CB
On 11/8/11 6:57 PM, Karen Lewellen wrote:
Hi folks,
For reasons that are complicated to explain I have the ear of the
legal department at paypal -ebay. Part of the reason is that, as some
of you may know, they are *requiring* all users to agree that that
they read pdf files, or they will lose their account. Because of this
and some other access issues with paypal and ebay, i have been asked
to document why things like pdf and captcha are issues for those using
adaptive tools. I have told them already that to assume everyone is
using jaws is impractical, and that still browsers like lynx, with its
recent edition dated June 2011, are good foundations for access. I
have shared that pdf reaains a hurtle, and captcha is flat out an
issue, as is stuff like flash.
because they are serious though I want to make maximum use of this
opportunity. What I would welcome is article information, places that
discuss why pdf for example and captcha remain barriers. Likewise
posts from you if you have met with issues with either service would
be welcome. I want them to fix this for everyone, not just sweep me
under the corporate rug. That they are shifting all document
responsibility t the end user is disturbing, since if you have an
issue say with security, you will bare the blame for any discrepancies
in documentation.
Additionally, if part of your professional life is access, share
under your professional umbrella. If I get enough research responses,
i will construct a solid document for them, and include as many other
people as I can.
Thanks in advance,
Karen
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